Isolation Techniques, Conidiation and Pathogenicity Studies of Ustilaginoidea virens Isolates (Uv3, Uv4, and Uv15) Causing False Smut in Rice

Abstract

Rice false smut, caused by Ustilaginoidea virens (U. virens), is a highly destructive disease that results in significant grain yield losses. This study focuses on three isolates of U. virens (Uv3, Uv4, and Uv15), examining their isolation, cultural morphology, conidiation media, and pathogenicity. During isolation from chlamydospores and mycelial discs of smut balls, Uv3, Uv4, and Uv15 displayed small mycelial growth and varied density at 7 days of incubation. Twenty-seven days after incubation, isolate Uv3 exhibited the highest growth at 77.00 mm, characterized by raised elevation and white-yellow surface color with yellow-green pigmentation. Isolate Uv4 showed circular growth with a mycelial growth of 64.00 mm, while isolate Uv15 displayed the lowest growth at 55.66 mm, with flat elevation and white-yellow-green appearance. In BPT 5204 rice leaf extract (BRLE), conidia count increased significantly with higher concentrations: Uv3 reaches 31.38x106 conidia/ml, Uv4 27.71x106 conidia/ml, and U15 20.11x106 conidia/ml. TN1 rice leaf extract (TRLE) media yields lower counts but shows similar concentration-dependent trends. PSB yields notably fewer conidia. Pathogenicity assessments on TN1 and BPT 5204 rice varieties revealed Uv3 as the most aggressive isolate, causing higher numbers of smut balls per panicle and greater grain infection percentages compared to Uv4 and Uv15.